Method of making rod-shaped particles for use as proppant and anti-flowback additive

ABSTRACT

A method for forming rod-shaped particles includes reducing a length of rods derived from a slurry made up of particles and a reactant, wherein the rods are in a stabilized state in which the reactant has been at least partially reacted with a coagulant, but the rods have not been sintered, and subsequently sintering the reduced length stabilized rods. The reducing the length of the stabilized rods includes subjecting the stabilized rods to mechanical vibration applied by a device, or feeding the stabilized rods through a device having a rotating cutting mechanism.

BACKGROUND

Hydrocarbons (such as oil, condensate, and gas) may be produced fromwells that are drilled into formations containing them. For a variety ofreasons, such as low permeability of the reservoirs or damage to theformation caused by drilling and completion of the well, or otherreasons resulting in low conductivity of the hydrocarbons to the well,the flow of hydrocarbons into the well may be undesirably low. In thiscase, the well is “stimulated,” for example, using hydraulic fracturing,chemical (such as an acid) stimulation, or a combination of the two(often referred to as acid fracturing or fracture acidizing).

Hydraulic and acid fracturing treatments may include two stages. A firststage comprises pumping a viscous fluid, called a pad, that is typicallyfree of proppants, into the formation at a rate and pressure high enoughto break down the formation to create fracture(s) therein. In asubsequent second stage, a proppant-laden slurry is pumped into theformation in order to transport proppant into the fracture(s) created inthe first stage. In “acid” fracturing, the second stage fluid maycontain an acid or other chemical, such as a chelating agent, that canassist in dissolving part of the rock, causing irregular etching of thefracture face and removal of some of the mineral matter, which resultsin the fracture not completely closing when the pumping is stopped.Occasionally, hydraulic fracturing may be done without a highlyviscosified fluid (such as water) to minimize the damage caused bypolymers or the cost of other viscosifiers. After finishing pumping, thefracture closes onto the proppant, which keeps the fracture open for theformation fluid (e.g., hydrocarbons) to flow to the wellbore of thewell.

Proppant is typically made of materials such as sand, glass beads,ceramic beads, or other materials. Sand is used frequently as theproppant for fracture treatments. However, for fractures with highclosure stress, such as greater than 6,000 pound per square inch (psi),in deep wells or wells with high formation forces, higher strengthproppant is desired. The closure stress that sand can sustain isnormally about 6,000 psi, so a closure stress over 6,000 psi could crushthe sand into fine particles and collapse the sand pack, which resultsin insufficient conductivity for the formation fluid to flow to thewellbore. Furthermore, the fine particles may continually flow backduring production of the well, and thus the conductivity of the wellwould reduce further, which results in a short useful life of the wellor results in a need for costly refracturing of the well.

Ceramic proppant has been used to maintain the conductivity of the wellswith a high closure stress. Typically, the higher the alumina (Al₂O₃)content, the higher the hardness and toughness of the ceramic proppant,but also the higher the specific gravity. A high specific gravity maylead to quick gravitational settling of the proppant, which results indifficulty to transport the proppant into the fracture, especially forlocations far from the wellbore. Also, quick settling in the fractureleads to lack of proppant on the top part of a fracture, which reducesthe productivity of the well. To transport proppant of high specificgravity with fracturing fluid of a low viscosity, fiber can be added tothe fluid as an additive. See, for example, U.S. Pat. No. 8,657,002,incorporated herein by reference in its entirety. To use fibereffectively for transporting proppant, the interaction force betweenfiber and proppant is important.

Other proppant shapes have been proposed for hydraulic fracturingapplications such as plate-like proppant (U.S. Patent ApplicationPublication No. 2011/0180259) and rod-shaped proppant (U.S. Pat. No.8,562,900). The rod-shaped proppant described in U.S. Pat. No. 8,562,900is made by extruding a mixture containing alumina-containing materials,a binding agent, a solvent, and other additives such as lubricants andplasticizers through a die. The mixture is not flowable and thus afterextruding, the rod shape is maintained. After drying or after sintering,the extruded rod is cut into desired length suitable to use as proppant.

The so-called drip-casting manufacturing technique has been adapted forthe manufacture of spherical ceramic proppants. Drip-casting substitutesconventional ways of pelletizing (also called granulating) ceramicproppant such as using high intensity mixers and pan granulators.Vibration-induced dripping (or drip-casting) was first developed toproduce nuclear fuel pellets. See U.S. Pat. No. 4,060,497. It hassubsequently evolved into applications for metal and ceramicmicrospheres for grinding media, pharmaceuticals and food industry. Anapplication of vibration-induced dripping to aluminum oxide spheres isdescribed in U.S. Pat. No. 5,500,162. The production of the microspheresis achieved through vibration-provoked dripping of a chemical solutionthrough a nozzle. The falling drops are surrounded by a reaction gas,which causes the droplet to gel prior to entering the reaction liquid(to further gel). Using a similar approach, U.S. Pat. No. 6,197,073covers the production of aluminum oxide beads by flowing a sol orsuspension of aluminum oxide through a vibrating nozzle plate to formdroplets that are pre-solidified with gaseous ammonia before their dropinto ammonia solution. U.S. Patent Application Publication No.2006/0016598 describes the drip-casting to manufacture a high-strength,light-weight ceramic proppant. U.S. Pat. No. 8,883,693 describes theapplication of the drip-casting process to make ceramic proppant.

Co-pending U.S. patent application Ser. No. 14/946,085, filed Nov. 19,2015, incorporated herein by reference in its entirety, describes amethod for forming rod-shaped particles comprising inducing flow of aslurry comprised of particles and a reactant through one or moreorifices and into a coagulation solution, wherein the slurry exiting theone or more orifices is a continuous uninterrupted stream; coagulatingthe reactant in the coagulation solution to form stabilized rods; dryingthe stabilized rods; and reducing a length of the dried stabilized rods.The rod-shaped particles after sintering may be used for applicationssuch as downhole application, for example including as proppants and asanti-flowback additives.

SUMMARY

This summary is provided to introduce a selection of concepts that arefurther described below in the detailed description. This summary is notintended to identify key or essential features of the claimed subjectmatter, nor is it intended to be used as an aid in limiting the scope ofthe claimed subject matter.

What is still desired is a convenient and cost effective method offorming rod-shaped particles able to perform well in downholeapplications in fracture formation, for example as a proppant and/or asan anti-flowback additive.

Described herein is a method for forming rod-shaped particles comprisingreducing a length of rods derived from a slurry comprised of particlesand a reactant, wherein the rods are in a stabilized state in which thereactant has been at least partially reacted with a coagulant, but therods have not been sintered; and subsequently sintering the reducedlength stabilized rods.

Also described is a method for forming rod-shaped particles comprisinginducing flow of a slurry comprised of particles and a reactant throughone or more orifices and into a coagulation solution, wherein the slurryexiting the one or more orifices is a continuous uninterrupted streamuntil rods of a desired length are formed, at least partiallycoagulating the reactant of the rods in the coagulation solution to formstabilized rods, reducing a length of the stabilized rods by subjectingthe stabilized rods to mechanical vibration applied by a device or byfeeding the stabilized rods through a device having a rotating cuttingmechanism, and subsequently sintering the reduced length stabilizedrods.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic of an example apparatus for forming continuousrods.

FIGS. 2-5 illustrate example devices for applying mechanical vibrationto stabilized rods to reduce the length thereof.

FIG. 6 illustrates an example device for cutting stabilized rods.

FIG. 7 is a graph illustrating an example of size reduction as afunction of time with the application of a mechanical vibration to thestabilized rods.

DETAILED DESCRIPTION

In the following description, numerous details are set forth to providean understanding of the present disclosure. However, it may beunderstood by those skilled in the art that the methods of the presentdisclosure may be practiced without these details and that numerousvariations or modifications from the described embodiments may bepossible.

At the outset, it should be noted that in the development of any suchactual embodiment, numerous implementation-specific decisions may bemade to achieve the developer's specific goals, such as compliance withsystem related and business related constraints, which will vary fromone implementation to another. Moreover, it will be appreciated thatsuch a development effort might be complex and time consuming but wouldnevertheless be a routine undertaking for those of ordinary skill in theart having the benefit of this disclosure. In addition, the compositionused/disclosed herein can also comprise some components other than thosecited. In the summary and this detailed description, each numericalvalue should be read once as modified by the term “about” (unlessalready expressly so modified), and then read again as not so modifiedunless otherwise indicated in context. The term about should beunderstood as any amount or range within 10% of the recited amount orrange (for example, a range from about 1 to about 10 encompasses a rangefrom 0.9 to 11). Also, in the summary and this detailed description, itshould be understood that a range listed or described as being useful,suitable, or the like, is intended to include support for anyconceivable sub-range within the range at least because every pointwithin the range, including the end points, is to be considered ashaving been stated. For example, “a range of from 1 to 10” is to be readas indicating each possible number along the continuum between about 1and about 10. Furthermore, one or more of the data points in the presentexamples may be combined together, or may be combined with one of thedata points in the specification to create a range, and thus includeeach possible value or number within this range. Thus, (1) even ifnumerous specific data points within the range are explicitlyidentified, (2) even if reference is made to a few specific data pointswithin the range, or (3) even when no data points within the range areexplicitly identified, it is to be understood (i) that the inventorsappreciate and understand that any conceivable data point within therange is to be considered to have been specified, and (ii) that theinventors possessed knowledge of the entire range, each conceivablesub-range within the range, and each conceivable point within the range.Furthermore, the subject matter of this application illustrativelydisclosed herein suitably may be practiced in the absence of anyelement(s) that are not specifically disclosed herein.

The present disclosure relates to methods of making rod-shapedparticles, to the rod-shaped particles made by such methods, and totreatment fluids that contain the rod-shaped particles made by suchmethods, wherein the rod-shaped particles may function as, for example,proppants and/or anti-flowback additives.

While in embodiments the rod-shaped particles herein are used in thecontext of a treatment fluid, for example as a proppant material and/oranti-flowback additive, it is not intended that the rod-shaped particlesas described herein be limited to being proppants and/or anti-flowbackadditives in such treatment fluids.

As used herein, the term “treatment fluid” refers to any pumpable and/orflowable fluid used in a subterranean operation in conjunction with adesired function and/or for a desired purpose. In some embodiments, thepumpable and/or flowable treatment fluid may have any suitableviscosity, such as a viscosity of from about 1 cP to about 10,000 cP,such as from about 10 cP to about 1000 cP, or from about 10 cP to about100 cP, at the treating temperature, which may range from a surfacetemperature to a bottom-hole static (reservoir) temperature, such asfrom about 0° C. to about 200° C., or from about 10° C. to about 120°C., or from about 25° C. to about 100° C., and a shear rate (for thedefinition of shear rate reference is made to, for example, Introductionto Rheology, Barnes, H.; Hutton, J. F; Walters, K. Elsevier, 1989, thedisclosure of which is herein incorporated by reference in its entirety)in a range of from about 1 s⁻¹ to about 1000 s⁻¹, such as a shear ratein a range of from about 100 s⁻¹ to about 1000 s⁻¹, or a shear rate in arange of from about 50 s⁻¹ to about 500 s⁻¹ as measured by commonmethods, such as those described in textbooks on rheology, including,for example, Rheology: Principles, Measurements and Applications,Macosko, C. W., VCH Publishers, Inc. 1994, the disclosure of which isherein incorporated by reference in its entirety.

As used herein, the term “rod-shaped particle” or “rod-shaped particles”refers to a particle(s) having a geometrically shaped cross-section anddimensions in which a length of the particle(s) is greater than across-sectional width of the particle(s). In embodiments, thecross-sectional geometric shape is substantially circular, and therod-shaped particle has a length that is greater than thecross-sectional diameter of the particle. The average length towidth/diameter ratio may be at least 2:1. The rod-shaped particles arenot limited to having a cross-sectional geometric shape of circular, andother cross-sectional shapes may be used, such as triangular orrectangular. Further, the rod-shaped particle may be substantiallystraight over the length of the particle, or the particle may have adegree of curvature over the length of the particle.

As will be described herein, the rod-shaped particles are derived fromrods that are reduced in length. “Rods” as used herein refers to rodsthat may be formed by inducing flow of a slurry comprised of particlesand a reactant through one or more orifices and into a coagulationsolution, wherein the slurry exiting the one or more orifices is acontinuous uninterrupted stream. “Continuous uninterrupted stream” inthis regard refers to an unbroken stream of desired length of the slurryin rod form. The slurry flow through the one or more orifices may becontinued until rods of a desired length are obtained. There is nolimitation on the length of the continuous rods as initially formed.

The method of forming the rods is first described. In embodiments, therods are formed by inducing flow of a slurry comprised of particles anda reactant through one or more orifices and into a coagulation solution,wherein the slurry exiting the one or more orifices is a continuousuninterrupted stream until rods of a desired length are formed, and atleast partially coagulating the reactant of the rods in the coagulationsolution to form stabilized rods.

In embodiments, the method further comprises forming the slurry ofparticles and reactant by mixing. As the particles, the particles may bemade of any suitable material, such as, for example, ceramic materials,sand, non-ceramic materials, composites of ceramic reinforced withadditional stronger materials and the like. As the ceramic particles ofthe slurry, any suitable ceramic material may be used, for exampleglass, and ceramic oxides such as alumina, bauxite, aluminum hydroxide,pseudo boehmite, kaolin, kaolinite, silica, silicates, clay, talc,magnesia and mullite. The ceramic particles may includealumina-containing particles or magnesium-containing particles. Theceramic particles may also be a composite particle that is comprised ofceramic reinforced with higher strength materials, which may be ceramicor non-ceramic, for example such as titanium carbide, carbon nanotubesor reinforcement elements such as fibers or polymers. Where therod-shaped particles may be used as a proppant that may need towithstand a higher fracture closure stress, for example of 6,000 psi ormore, alumina-containing particles are desired because rod-shapedparticles derived from alumina-containing particles have a higherstrength and toughness. Typically, the higher the alumina (Al₂O₃)content, the higher the strength, hardness and toughness of therod-shaped particles. In embodiments, the ceramic particles may have analumina content of from, for example, 5% to 95% by weight alumina, suchas 20% to 75% by weight or 30% to 75% by weight.

While the particles may have any suitable size, an average size of lessthan 500 microns, such as an average size of 0.01 to 100 microns or 0.01to 50 microns, may be desirable. The particles (i.e., the raw materialfor the rod-shaped particles) are desirably sized depending on theorifice diameter through which the slurry will pass in forming therod-shaped particles, and the orifice diameter may be equal to orgreater than, for example, ten times the raw material particle averagediameter.

The reactant in the slurry may be any material that can be coagulated,gelled and/or cross-linked by another material that is present in thecoagulation solution. Reactants are typically organic materials used tostabilize the shape of the slurry once it is formed into the desired rodshape. The reactants thus react to form a solid or semi-solid shapedproduct once exposed to the coagulation solution. Examples of suitablereactants include, for example, polyvinyl alcohol, polyvinyl acetate,methylcellulose, dextrin, polysaccharides such as alginates, for examplesodium alginate, and molasses. Sodium alginate is a naturally occurringpolysaccharide that is soluble in water as the sodium salt, and is asuitable reactant in the methods described herein. The reactant may beincluded in the slurry in an amount of from 0.01% to 25%, such as 0.01%to 5% or 0.01% to 1% by weight of the slurry. The solids content of theslurry may be from, for example, 10% to 95%, such as 15% to 90% or 20%to 90%. The solids content may be adjusted so that the slurry has asuitable viscosity for flow through the one or more orifices, such as aviscosity of 1 to 10,000 cP measured at a shear rate of 100 (1/s).

The slurry may also contain one or more solvents. Possible solvents thatcan be used include water, alcohols, and ketones. Other additives mayalso be included in the slurry, such as lubricants and dispersants.Lubricants may include one or more of Manhattan fish oil, wax emulsions,ammonium stearates, and wax. Dispersants may include one or more of acolloid, polyelectrolyte, tetra sodium pyrophosphate, tetra potassiumpyrophosphate, polyphosphate, ammonium citrate, ferric ammonium citrate,hexametaphosphate, sodium silicate, ammonium polyacrylate, sodiumpolymethacrylate, sodium citrate, sodium polysulfonate orhexametaphosphate salt, as well as any surfactant.

The slurry may be housed in a container that is associated with the oneor more orifices. The slurry is induced to flow from the container tothe one or more orifices by any suitable method. For example, the slurrymay be induced to flow from the container by applying a load to a pistonin the container housing the slurry to force the slurry out an exit portof the container that is associated with the one or more orifices. Also,increasing pressure in the container housing the slurry by any suitablemethod, and/or decreasing a volume of the container housing the slurryby any suitable method, to force the slurry to exit the container at aport associated with the one or more orifices may also be used. Theslurry may also be pumped from the container housing the slurry to theone or more orifices associated with an exit of the container.

The exit port of the container may be connected to a pipe through whichthe slurry flows to the one or more orifices. Alternatively, the exitport may directly feed the slurry to the one or more orifices.

The one or more orifices may be comprised of a single orifice for makinga single, continuous rod form or may be comprised of multiple orificesthat each makes a single, continuous rod form. Each orifice may be inthe form of, for example, an opening in a membrane. Alternatively, theone or more orifices may be in the form of a spinneret such as used infiber spinning (see, for example, U.S. Pat. No. 8,529,237, incorporatedherein by reference). Each orifice has a size that will substantiallycorrespond to the cross-sectional size, such as cross-sectional diameteror width, of the end rod-shaped particles. For rods with a circularshape cross-section, for example, the diameter can be controlled by thesize of the orifice, the jetting rate of the slurry, the moving speed ofthe orifices, and the rheological properties of the slurry.

The one or more orifices can be used to impart a cross-sectional shapeto the rod-shaped particles. For example, the one or more orifices mayhave a shape such as circle, ellipse, oval, multifoil, triangle,rectangle and the like. As the slurry is flowed through the orifice, theshape of the orifice will be imparted to the slurry such that the rodswill have a corresponding cross-sectional shape. In this manner, therod-shaped particles can be made to have a cross-sectional shape such ascircle, ellipse, oval, multifoil, triangle, rectangle and the like.

In addition, a vibration may be applied to the orifices as the slurryflows through the orifices in order to impart an inhomogeneouscross-section along the length of the formed rods. For example,vibrating the orifices by a mechanical means during flowing of theslurry, where the vibration frequency is maintained to a low enoughfrequency to avoid completely severing the flow, that is, withoutbreaking the continuous flow into separate segments, can alter thecross-section of the rods along the length of the rod. As an example,the vibration can be intermittently applied to thin or thicken (makesmaller or bigger) the cross-sectional diameter at points along thelength of the continuous rod. When the orifice moves in the samedirection of the slurry flow, the cross-section will become thicker, andwhen the orifice moves in the opposite direction of the slurry flow, thecross-section will become thinner. A suitable range of frequencies forthe vibration to thin or thicken the cross-section is, for example,0.01-100 Hz, as long as the slurry flow is not severed. In addition tothe frequency, the vibration amplitude, slurry composition, flow speedand orifice size may also be taken into consideration in determining thefrequency of the vibration to be applied.

The orifices may be located above the coagulation solution, or may beimmersed in the coagulation solution. The orifices may be fixed in asingle position during flowing of the slurry therethrough, or, inembodiments, the orifices may be made to move in a vertical directionwith respect to the surface of the coagulation solution. In this manner,the orifices may be made to move in and out of the coagulation solutionduring the flowing of the slurry therethrough. In still furtherembodiments, the orifices may be made to move in a horizontal manner, orlaterally, with respect to a surface of the coagulation solution whilethe slurry is flowing therethrough. This may allow for the continuousuninterrupted rods to be organized, or aligned, within the coagulationsolution. For example, if the orifices are moved in a circular patternwhile the slurry is fed therethrough, the rods may be stacked in acircular pattern within the coagulation solution. This may also be usedto impart controlled curvature to the rods, and thus ultimately to therod-shaped particles. As a further example, moving the orifices back andforth in a horizontal manner can stack the rods in such a way that theindividual stacks of rods can be readily gathered for subsequentprocessing.

To achieve rods of a desired length before size reduction, a periodicspike vibration may be applied to the one or more orifices when anamount of slurry that has passed through the one or more orifices issuch that the slurry having exited through the one or more orifices hasa predetermined length. Whereas above a low vibration frequency waspossibly applied to thin but not sever the continuous flow, here theperiodic spike vibration is sufficient to sever the continuous flow atthe orifices.

The coagulation solution comprises a coagulant that interacts with thereactant in the slurry to at least partially coagulate, gel and/orcross-link the reactant, thereby forming the slurry into a solid orsemi-solid product, referred to herein as a “stabilized rod.” Thus, whenthe slurry comes into contact with the coagulation liquid, thecoagulation liquid interacts with the reactant in the slurry tostabilize the shape imparted to the slurry by passing through theorifices. The slurry described herein is rather flowable, and the rodshape is stabilized by chemical reaction at least on the surface of theshaped slurry. Some examples of useful coagulation liquids, for examplefor use with sodium alginate as a reactant, include, but are not limitedto, a calcium salt such as calcium chloride solution at suitableconcentration of calcium chloride, or an aluminum chloride hexahydratesolution. The amount of coagulant to include in the solution shoulddesirably be sufficient at a minimum to coagulate, gel and/or cross-linkthe reactant and at a maximum should desirably not exceed theconcentration that will dissolve into the solution. For example, asuitable concentration of the coagulant in the coagulation solution maybe, for example, 0.1% to 25%, such as 0.1% to 10% by weight of thecoagulation solution.

The slurry may be flowed through the orifices at such a rate that theslurry is maintained in the continuous uninterrupted state as it exitsthe orifices. If the orifices are located above the coagulationsolution, the flowing rate of the slurry may be over a value for thejetting stream of slurry to not only maintain the continuousuninterrupted state but also to penetrate the solution surface and jetinto the solution. The value depends not only on the viscosity anddensity of the slurry but also on the size of the orifice, the distanceof the orifice to the coagulation solution, the capillary force and thedensity of the coagulation solution. A typical value of flowing speed inthis arrangement of the orifices may be 1.5 m/s for an alumina slurrymade up of 75% by weight of solids, a coagulating solution at aconcentration level of 2% by weight, and an orifice size of 0.8 mm indiameter, and a height of 5 mm. If the orifices are located in thecoagulation solution, the flowing rate of the slurry suitable formanufacturing the rod-shaped proppant can be, for example, from 0.01 m/sto 5 m/s for an orifice of 0.37 mm in diameter and a slurry compositionas in the example discussed immediately above.

As discussed above, the shaped slurry exiting the orifices is in a formof a continuous uninterrupted stream, and is flowed such that it eitherexits the orifices directly into the coagulation solution in which theorifices are immersed, or is made to penetrate into the coagulationsolution when the orifices are located above the coagulation solution,thereby at least partially coagulating the reactant in order to formstabilized rods. The stabilized rods have a quasi-rigid form withsufficient stiffness to be handled without losing their shape.

FIG. 1 is a schematic of one apparatus that may be used for carrying outthe above-described method. In FIG. 1, the slurry (4) housed incontainer (2) is forced to flow by applying a load (1) on a piston (3).When the load is applied to the slurry, the slurry is made to flow outan exit port at the bottom of the container and into tube or pipe (5)that is connected with an orifice (6). In this case, the orifice isimmersed in the coagulation solution (8). The slurry exits the orificeas a continuous uninterrupted rod (9). Also shown in FIG. 1 is theoption for the orifice to be moved from side to side in a horizontaldirection (7) with respect to the surface of the coagulation solution,thereby stacking the continuous rod (9) in an organized manner withinthe coagulation solution.

The stabilized rods are collected from the coagulation solution by anysuitable methodology. The collected stabilized rods may optionally bedried using any suitable drying processes. For example, the stabilizedrods may be subjected to air drying, or to drying using electric or gasdriers.

After any optional drying step, but before any final step to increasethe strength of the end rod-like particles such as sintering, the rodsare subjected to a step of reducing a length of the stabilized rods. Inthis regard, the pre-sintered, stabilized rods may be subjected tomechanical vibration applied by a device or may be fed through a devicehaving a rotating cutting mechanism.

As mentioned above, the stabilized rods possess enough stiffness to keepa quasi-rigid form. This stability of the pre-sintered stabilized rodsopens the opportunity for novel methods to break the rods into the endrod-shaped particles of desired length. Once the stiff, rod-likeparticles have been severed to desired length distributions, therod-shaped particles may be sintered, or subjected to some alternativesuitable strength increasing process, to achieve higher strengths sothat the rod-shaped particles are suitable for use in downholeapplications, for example as proppants or anti-flowback additives.

A first method of reducing a length of the stabilized rods is bysubjecting the stabilized rods to mechanical vibration applied by adevice. The device may be, for example, a vessel of any suitable size,and the stabilized rods are loaded into the vessel and vibrationalenergy is applied to the loaded vessel. Vessels may have a height offrom 1 cm to 5 m, and a volume of from about 1 cm³ to about 5 m³. Theinterior of the vessel may be made of any suitable hard or roughmaterial, such as, for example, glass, ceramics, polymers or metals. Thestabilized rods may be loaded to fill any volume of the vessel, forexample the stabilized rods may be loaded to occupy from about 5% toabout 95%, such as form about 5% to about 75%, by volume of the vessel.

In embodiments, the vessel is a closed vessel, which can assist inreducing the introduction of debris or dust from the mechanicalvibration into the atmosphere. The vessel is not limited to beingclosed, however, and may also be open. The applying of the mechanicalenergy can be done on a batch basis, with the mechanical energy beingapplied to a single load of rods until rod-shaped particles of a desiredlength are obtained, or the applying of the mechanical energy may bedone on a continuous basis, with additional rods being introducedcontinuously or at least at regular intervals, with rod-shaped particlesbeing removed from the vessel as the particles reach a desired size.This removal may be accomplished through the use of sieves locatedwithin the vessel, as will be further explained below.

FIGS. 2-5 illustrate various embodiments of possible vessels for useherein. The interior walls of the vessel may be flat and relativelysmooth, or as in the vessel of FIG. 2, the vessel 20 may include aplurality of protuberances 25 along one or more interior walls of thevessel. The protuberances may take any suitable form and occur on theinterior walls in any frequency, the protuberances enhancing thebreaking efficiency of the vessel.

As shown in FIGS. 3 and 4, the vessel 20 may also include structureswithin the interior space of the vessel to increase the breakingefficiency. The vessel 20 of FIG. 3 includes bars 35 extending from atleast one interior wall of the vessel and extending fully across aninterior of the vessel. Although a plurality of bars is shown in FIG. 3,one bar may be used if desired. In FIG. 4, the bars extend onlypartially across the interior space of the vessel. In this embodiment,the bars may have end pads 36 at the distal ends of the bars in theinterior space, the pads increasing the surface area of the bars tofurther increase the efficiency of the size reduction process. The barsand pads may be comprised of materials such as glass, ceramics, polymersand/or metals.

One or more sieves may be included in the vessel, for example at a baseportion of the vessel as shown in FIG. 5 with sieves 40 and 45. Thesieves may be mounted in the vessel by any suitable means, for examplethrough the use of peripheral rims or slots. The sieves are used toseparate out the rods with desired length during the application ofvibrational energy to the vessel. As an example shown in FIG. 5, twosieves 40 and 45 are added to vessel 20, with peripheral rims 48 used tosupport the sieves, and also enabling ease of installation andreplacement of the sieves. By choosing the sieve mesh based on thediameter of the rods and by controlling the distance and alignmentbetween the sieves, only rod-shaped particles with a length less than acertain value can pass through the lower sieve and be separated from thevessel. The rod-shaped particles are thus able to exit the vessel whenable to pass through a sieve having the smallest size opening, which canbe set to be the same as the desired end size of the rod-shapedparticles.

The features of the vessels shown in FIGS. 2-5 may be combined in anysuitable combination in a single vessel. For example, a vessel mayinclude protuberances and rods, protuberances and sieves, orprotuberances, rods and sieves.

The mechanical energy may be applied to the vessel by any suitablemeans, for example through the mounting of the vessel on a vibrationsystem that has a controllable vibration amplitude and frequency. Theamplitude of the applied mechanical vibrational energy may be from, forexample, 0.01 mm to 10 cm and the frequency may be from, for example, 10Hz to 10,000 Hz, although values outside of these ranges may also besuitably used.

Through the application of the mechanical vibration, the pre-sinteredstabilized rods hit each other and the interior walls of the vessel, andthus break into shorter lengths.

To further enhance the breaking efficiency, breaking media may be addedto the vessel if desired. The media may be made of any kind of solidmaterials such as glass, natural/sintered ceramic, metals such as steel,and polymers. Also, the media may have any kind of shape, such asparticle, rod or ring. The average size of the media may be from, forexample, 1 mm to 1 m.

Advantages of reducing the size of the pre-sintered stabilized rodsthrough the application of mechanical vibration include that all therods placed in the vessel are subjected to the shaking or vibrationalenergy and can break into short length at the same time. Further, longerrods are easier to break than shorter rods due to applied bendingforces, so with more shaking time, the range of the length distributiondecreases and the average size is reduced. The vibrational energyamplitude and frequency may be selected in the process to achieve adesired length distribution.

The stabilized rods may be subjected to the mechanical vibration for anysuitable amount of time in order to achieve rod-shaped particles of thedesired size. An example range for a period of applying vibrationalenergy to the vessel may be from 0.1 minutes to 30 minutes, such as 0.1minutes to 10 minutes. It has been found that the size of the rod-shapedparticles typically levels off (reaches a plateau state) at some point,and further size reduction at a given vibrational energy does not occur.For example, FIG. 7 illustrates the average length of the rods as afunction of time subjected to vibrational energy, and shows a plateauingof average length over time. If further size reduction is desired whereplateauing has occurred, the vibrational energy applied can beincreased, or breaking media may be introduced, to affect further sizereduction.

A second method of reducing a length of the stabilized rods is byfeeding the stabilized rods through a device having a rotating cuttingmechanism. A suitable device would have a design in which the stabilizedrods are dropped vertically through the device and encounter therotating cutting mechanism as the stabilized rods fall through thedevice. As the rotating cutting mechanism within the device, anysuitable rotating cutting mechanism may be used, such as a cuttingmechanism having one or more bars, with or without pads at a distal endthereof, extending from a rotating spine. The spine may be made torotate by being attached to, for example, a driving motor, which can beoperated at any desirable rate of rotation, for example from 1 rpm to10,000 rpm or more, and can be rotated either clockwise orcounterclockwise.

An example device having a rotating cutting mechanism is illustrated inFIG. 6. In the FIG. 6 device, spine 51 is attached to motor 60, and aplurality of bars 52 extend from the spine and across the cuttingchamber 53 of the device. The spine and bars are made to rotate by themotor. The stabilized rods to be cut are fed through the feeding funnel54 and into the cutting chamber 53. After being fed into the chamber,the stabilized rods contact the rotating bars 52 as they fall throughthe cutting chamber, and the length of the stabilized rods is therebyreduced. The number of the cutting bars is not limited, and may bevaried between 1 to 100 or more. Also, the bars can be of any shape,length and diameter, including different shapes, lengths and diametersamong different bars, distributed in any direction, and made of anymaterials such as metal, for example steel or alloys, ceramics andpolymers.

The device may also include features such as a collection mechanism forthe rod-shaped stabilized particles and a dust reduction mechanism. Forexample, as shown in FIG. 6, as the rod-shaped particles of desired sizeexit the cutting chamber, the rods may exit the device onto atransporting belt 59 or may exit directly into a collection vessel (notshown). Further, at or near the point of exit from the cutting chamber,a conduit 55 may be located to connect the cutting chamber with a dustcollection chamber 56. Conduit 57 may be associated with the dustcollection chamber to provide a connection with, for example, a vacuumpump 58. A filter 61 may be mounted at the entrance end of the conduitto the dust collection chamber. The power of the vacuum pump may becontrolled so only dust is collected in the dust collection chamber,while permitting the rod-shaped particles to exit the cutting chamber tothe point of collection without being collected by the dust collectionchamber.

The end size of the rod-shaped particles may be controlled throughcontrol of the number, size and shape of the cutting bars, and therotational speed of the cutting bars, and the length of the cuttingchamber.

Upon collection, the rod-shaped particles may be subjected to sieving toensure that the rod-shaped particles have the desired size. Larger sizedrod-shaped particles unable to pass through the sieve may be collectedand re-introduced back through the rotating cutting device untilrod-shaped particles of the desired size are obtained.

Advantages that may be realized with the use of the rotating cuttingmechanism include, for example, that the device can be added to theproduction line of rod-shaped particles for continual particlemanufacture. Further, by selecting the shape, the number, and therotating speed of the cutting bars, pre-sintered stabilized rods of anylength and diameter may be reduced to a desired length for using asproppant and anti-flowback additives after sintering.

After the rod-shaped particles of a desired size are obtained, therod-shaped particles are then desirably subjected to a strengthincreasing treatment. For example, the rod-shaped particles may besubjected to sintering. Sintering may be conducted at a temperature offrom, for example, about 800° C. to about 2,300° C., such as from about1,200° C. to about 1,700° C.

The end size-reduced rod-shaped particles may have an average length of0.2 mm to 5 cm, an average diameter (or cross-sectional width) of 0.1 mmto 1 cm, and an average length to diameter of at least 2:1. Therod-shaped particles desirably have an average length of 0.2 mm to 5 cm,for example from 0.2 mm to 1 cm or from 0.2 mm to 50 mm. The rod-shapedparticles desirably have an average diameter (or cross-sectional width)of 0.1 mm to 1 cm, for example from 0.1 mm to 5 mm or 0.1 mm to 1 mm.The rod-shaped particles have an average length to diameter (or width)of at least 2:1, for example of 5:1 to 1,000:1 or 5:1 to 100:1.

The rod-shaped particles made by the methods herein possess a number ofdesirable properties compared to conventional spherical proppants andanti-flowback additives.

Where the rod-shaped particles are used as proppant in a treatmentfluid, compared to conventional spherically shaped proppant, therod-shaped particles disclosed herein may interlock with fiber includedin the treatment fluid, as well as interlock with themselves, achievinga lower settling rate, and thus can be more easily transported intofractures. Fracturing methodologies that use fibers in the fracturingfluid typically rely on proppant clusters/pillars to maintain the widthof a fracture and channels for conducting the formation fluid. Pillarswith low strength may spread and collapse under closure stress, whichreduces the channel size and/or eliminates the channels. Theinterlocking of the rod-shaped particles herein with the fibers and withthemselves may increase the strength of the pillars, compared to the useof spherical proppant with a similar surface texture.

Besides the strength of the proppant, a tight packing may inhibit theflow of the formation fluid to the wellbore. The way of packing candepend on the shape of the proppant. The rod-shaped particles disclosedherein may interlock with each other, thereby reducing their mobility,which in turn may help to maintain an adequate level of porosity andconductivity for formation fluids such as oil and/or gas to flow.

The rod-shaped particles described herein may thus be harder to flowback compared to spherically shaped proppant. The particles can be usedtogether with other shaped proppants as an anti-flowback additive. Theparticles can also be used together with fiber to achieve enhancedanti-flowback control.

Packs of the rod-shaped particles in a fracture can have highconductivity due to high porosity resulting from mechanisms of theparticles' interlocking.

The mechanical interactions of rod-shaped particles with themselvesand/or with fiber may increase the capability of the fiber to transportproppant into the fracture during a fracturing treatment and also mayincrease the strength of pillars when the fracture walls close onto thepillars.

In some embodiments, the concentration of the rod-shaped particles inthe treatment fluid may be any desired value, such as a concentration inthe range of from about 0.01 to about 80% by weight of the treatmentfluid, or a concentration in the range of from about 0.1 to about 25% byweight of the treatment fluid, or a concentration in the range of fromabout 1 to about 10% by weight of the treatment fluid.

Although the rod-shaped particles may be used by themselves in thefluid, for example as proppants for a fracture, they may also be usedtogether with conventional proppants, for example with sphericalproppant particles of glass, sand, ceramic and the like. Other proppantparticles may be used in a weight ratio of the rod-shaped particles tothe other proppant particles of from 0.1:1 to 10:1. In some embodiments,other proppants may include sand, synthetic inorganic proppants, coatedproppants, uncoated proppants, resin coated proppants, and resin coatedsand. The proppants may be natural or synthetic (including silicondioxide, sand, nut hulls, walnut shells, bauxites, sintered bauxites,glass, natural materials, plastic beads, particulate metals, drillcuttings, ceramic materials, and any combination thereof), coated, orcontain chemicals; more than one may be used sequentially or in mixturesof different sizes or different materials. The proppant may be resincoated. The rod-shaped particles may also be resin coated, wheredesired.

In some embodiments, the treatment fluids may also include a fibrousmaterial, as well known in the art. Fibers may be included in thetreatment fluid in order to assist in transport of the rod-shapedparticles into the fractures. For example, the treatment fluid maycomprise rod-shaped particles and a fiber of any desired thickness(diameter), density and concentration that is effective to assist in thedownhole operation. The fiber may be one or more member selected fromnatural fibers, synthetic organic fibers, glass fibers, ceramic fibers,carbon fibers, inorganic fibers, metal fibers, or a coated form of anyof the above fibers.

Fibers may be used in bundles. The fibers may have a length in the rangeof from about 1 mm to about 30 mm, such as in the range of from about 5mm to about 20 mm. The fibers may have any suitable diameter or crossdimension (shortest dimension), such as a diameter of from about 5 to500 microns, or a diameter of from about 20 to 100 microns, and/or adenier of from about 0.1 to about 20, or a denier of from about 0.15 toabout 6.

The fibers may be formed from a degradable material or a non-degradablematerial. The fibers may be organic or inorganic. Non-degradablematerials are those wherein the fiber remains substantially in its solidform within the well fluids. Examples of such materials include glass,ceramics, basalt, carbon and carbon-based compound, metals and metalalloys. Polymers and plastics that are non-degradable may also be usedas non-degradable fibers. Such polymers and plastics that arenon-degradable may include high density plastic materials that are acidand oil-resistant and exhibit a crystallinity of greater than 10%.Degradable fibers may include those materials that can be softened,dissolved, reacted or otherwise made to degrade within the well fluids.Such materials may be soluble in aqueous fluids or in hydrocarbonfluids.

Suitable fibers may also include any fibrous material, such as, forexample, natural organic fibers, comminuted plant materials, syntheticpolymer fibers (by non-limiting example polyester, polyaramide,polyamide, novoloid or a novoloid-type polymer), fibrillated syntheticorganic fibers, ceramic fibers, inorganic fibers, metal fibers, metalfilaments, carbon fibers, glass fibers, ceramic fibers, natural polymerfibers, and any mixtures thereof.

The treatment fluid includes a carrier solvent that may be a puresolvent or a mixture. Suitable solvents may be aqueous or organic based.For example, the treatment fluid may include a carrier solvent and therod-shaped particles. The fluid may be any suitable fluid, such as, forexample, water, fresh water, produced water, seawater, or an aqueoussolvent, such as brine, mixtures of water and water-soluble organiccompounds and mixtures thereof. Other suitable examples of fluidsinclude hydratable gels, such as guars, poly-saccharides, xanthan,hydroxy-ethyl-cellulose; cross-linked hydratable gels, viscosified acid,an emulsified acid (such as with an oil outer phase), an energized fluid(including, for example, an N₂ or CO₂ based foam), and an oil-basedfluid including a gelled, foamed, or otherwise viscosified oil. Suitableorganic solvents that may act as a carrier solvent for the treatmentfluids of the disclosure include, for example, alcohols, glycols,esters, ketones, nitrites, amides, amines, cyclic ethers, glycol ethers,acetone, acetonitrile, 1-butanol, 2-butanol, 2-butanone, t-butylalcohol, cyclohexane, diethyl ether, diethylene glycol, diethyleneglycol dimethyl ether, 1,2-dimethoxyethane (DME), dimethylether,dibutylether, dimethyl sulfoxide (DMSO), dioxane, ethanol, ethylacetate, ethylene glycol, glycerin, heptanes, hexamethylphosphoroustriamide (HMPT), hexane, methanol, methyl t-butyl ether (MTBE),N-methyl-2-pyrrolidinone (NMP), nitromethane, pentane, petroleum ether(ligroine), 1-propanol, 2-propanol, pyridine, tetrahydrofuran (THF),toluene, triethyl amine, o-xylene, m-xylene, p-xylene, ethylene glycolmonobutyl ether, polyglycol ethers, pyrrolidones, N-(alkyl orcycloalkyl)-2-pyrrolidones, N-alkyl piperidones, N, N-dialkylalkanolamides, N,N,N′,N′-tetra alkyl ureas, dialkylsulfoxides,pyridines, hexaalkylphosphoric triamides,1,3-dimethyl-2-imidazolidinone, nitroalkanes, nitro-compounds ofaromatic hydrocarbons, sulfolanes, butyrolactones, alkylene carbonates,alkyl carbonates, N-(alkyl or cycloalkyl)-2-pyrrolidones, pyridine andalkylpyridines, diethylether, dimethoxyethane, methyl formate, ethylformate, methyl propionate, acetonitrile, benzonitrile,dimethylformamide, N-methylpyrrolidone, ethylene carbonate, dimethylcarbonate, propylene carbonate, diethyl carbonate, ethylmethylcarbonate, dibutyl carbonate, lactones, nitromethane, nitrobenzenesulfones, tetrahydrofuran, dioxane, dioxolane, methyltetrahydrofuran,dimethylsulfone, tetramethylene sulfone, diesel oil, kerosene,paraffinic oil, crude oil, liquefied petroleum gas (LPG), mineral oil,biodiesel, vegetable oil, animal oil, aromatic petroleum cuts, terpenes,mixtures thereof.

Treatment fluids may optionally comprise other chemically differentmaterials. In embodiments, the treatment fluid may further comprisestabilizing agents, surfactants, diverting agents, or other additives.Additionally, a treatment fluid may comprise a mixture of variouscrosslinking agents, and/or other additives, such as fibers or fillers.Furthermore, the treatment fluid may comprise buffers, pH controlagents, and various other additives added to promote the stability orthe functionality of the treatment fluid. The components of thetreatment fluid may be selected such that they may or may not react withthe subterranean formation that is to be treated.

In some embodiments, the treatment fluid may further have a viscosifyingagent. The viscosifying agent may be any crosslinked polymers. Thepolymer viscosifier can be a metal-crosslinked polymer. Suitablepolymers for making the metal-crosslinked polymer viscosifiers include,for example, polysaccharides such as substituted galactomannans, such asguar gums, high-molecular weight polysaccharides composed of mannose andgalactose sugars, or guar derivatives such as hydroxypropyl guar (HPG),carboxymethylhydroxypropyl guar (CMHPG) and carboxymethyl guar (CMG),hydrophobically modified guars, guar-containing compounds, and syntheticpolymers. Crosslinking agents based on boron, titanium, zirconium oraluminum complexes are typically used to increase the effectivemolecular weight of the polymer and make them better suited for use inhigh-temperature wells.

Other suitable classes of polymers that may be used as a viscosifyingagent include polyvinyl polymers, polymethacrylamides, cellulose ethers,lignosulfonates, and ammonium, alkali metal, and alkaline earth saltsthereof. Additional examples of other water soluble polymers that may beused as a viscosifying agent include acrylic acid-acrylamide copolymers,acrylic acid-methacrylamide copolymers, polyacrylamides, partiallyhydrolyzed polyacrylamides, partially hydrolyzed polymethacrylamides,polyvinyl alcohol, polyalkyleneoxides, other galactomannans,heteropolysaccharides obtained by the fermentation of starch-derivedsugar and ammonium and alkali metal salts thereof.

In some embodiments, the carrier fluid may optionally further compriseadditional additives, including, for example, acids, fluid loss controladditives, gas, corrosion inhibitors, scale inhibitors, catalysts, claycontrol agents, biocides, friction reducers, combinations thereof andthe like. For example, in some embodiments, it may be desired to foamthe composition using a gas, such as air, nitrogen, or carbon dioxide.

The foregoing is further illustrated by reference to the followingexamples, which are presented for purposes of illustration and are notintended to limit the scope of the present disclosure.

EXAMPLES

To prepare rod-shaped particles, the apparatus of FIG. 1 was used, withthe device including a single orifice immersed in the coagulationsolution. A sample slurry of 144 g water, 400 g ceramic raw powder(alumina-based), 1.6 g of sodium alginate, 0.8 g of dispersant(synthetic polyelectrolyte dispersing agent), 0.38 g of phosphate basedsurfactant and 0.48 g of lubricant (alkali-free pressing agent) wasprepared and used for illustration.

The coagulation solution was comprised of a 2 w % of calcium chloridesolution. The orifice had an orifice diameter of 0.8 mm, and the slurrywas fed through the orifice at a rate of 9 ml/min. The stabilized rodswere taken out from the coagulation solution and dried in an oven at 60°C. for 10 hours. 100 g of the dried rods, with an average diameter of0.8 mm, were placed in a plastic cylindrical vessel with an insideheight of 8 cm and diameter of 6 cm. The vessel was held by one hand andplaced on a VWR analog Vortex Mixer for shaking. With a shakingfrequency of 60 Hz and amplitude of 2 mm, the length of 300 to 700rod-shaped particles were measured after shaking for 0.25, 1, 3, and 5minutes. The length of the rod-shaped particles as a function of theshaking time is shown in FIG. 7. The average length and the range of thelength distribution decreased with shaking time until reaching a plateaustate, showing the effectiveness of reducing length of the particlesthrough shaking.

Although the preceding description has been set forth with reference toparticular means, materials and embodiments, it is not intended to belimited to the particulars disclosed herein; rather, it extends to allfunctionally equivalent structures, methods and uses, such as are withinthe scope of the appended claims. Furthermore, although only a fewexample embodiments have been described in detail above, those skilledin the art will readily appreciate that many modifications are possiblein the example embodiments without materially departing from thedisclosure herein. Accordingly, all such modifications are intended tobe included within the scope of this disclosure as defined in thefollowing claims. In the claims, means-plus-function clauses areintended to cover the structures described herein as performing therecited function and not only structural equivalents, but alsoequivalent structures. Thus, although a nail and a screw may not bestructural equivalents in that a nail employs a cylindrical surface tosecure wooden parts together, whereas a screw employs a helical surface,in the environment of fastening wooden parts, a nail and a screw may beequivalent structures.

What is claimed is:
 1. A method for forming rod-shaped particlescomprising: reducing a length of pre-sintered continuous rods derivedfrom a slurry comprised of particles and a reactant, wherein, prior tosintering, the rods are in a stabilized state in which the reactant hasbeen at least partially reacted with a coagulant, but the rods have notbeen sintered; and subsequently sintering the reduced length stabilizedrods.
 2. The method according to claim 1, wherein the reducing thelength of the stabilized rods comprises subjecting the stabilizedpre-sintered continuous rods to mechanical vibration applied by adevice.
 3. The method according to claim 2, wherein the mechanicalvibration is applied by a device comprising a vessel, wherein thestabilized pre-sintered continuous rods are loaded into the vessel andvibrational energy is applied to the loaded vessel.
 4. The methodaccording to claim 3, wherein the vessel includes a plurality ofprotuberances along one or more interior walls of the vessel.
 5. Themethod according to claim 3, wherein the vessel includes one or morebars extending from at least one interior wall of the vessel andextending partially or fully across an interior of the vessel.
 6. Themethod according to claim 3, wherein the vessel includes one or moresieves through which the reduced length stabilized pre-sintered rods canpass when the stabilized pre-sintered rods have a desired reducedlength.
 7. The method according to claim 1, wherein the reducing thelength of the stabilized rods comprises feeding the stabilizedpre-sintered continuous rods through a device having a rotating cuttingmechanism.
 8. The method according to claim 7, wherein the stabilizedpre-sintered continuous rods are dropped vertically through the deviceand encounter the rotating cutting mechanism as the stabilized rods fallthrough the device.
 9. The method according to claim 7, wherein therotating cutting mechanism comprises one or more bars extending from arotating spine.
 10. The method according to claim 1, wherein theparticles are ceramic particles.
 11. The method according to claim 1,wherein the reactant is an alginate and the coagulant comprises acalcium salt.
 12. The method according to claim 1, wherein the reducedlength rod-shaped particles have an average length of 0.1 mm to 5 cm, anaverage diameter of 0.2 mm to 1 cm and an average length to diameter ofat least 2:1.
 13. The method of claim 10, wherein the ceramic particleshave an alumina content between 5 wt % and 95 wt %.
 14. The method ofclaim 10, wherein the ceramic particles have an average size smallerthan 500 μm.
 15. The method of claim 2, wherein the mechanical vibrationhas a frequency between 0.01 Hz and 100 Hz.
 16. The method of claim 1,wherein the reactant is present in the slurry at a concentration between0.01% and 25%.
 17. The method of claim 1, wherein the slurry furthercomprises one or more solvents.
 18. The method of claim 1, wherein theslurry further comprises one or more lubricants.
 19. The method of claim1, wherein the slurry further comprises one or more dispersants.
 20. Themethod of claim 1, wherein the coagulant is present in a solution at aconcentration between 0.1% and 25%.